IdentityProviderPolicy may be incorrect

From #290710 (comment 459610359), I am developing a new cop.

It seems like ee/app/policies/ee/identity_provider_policy.rb has a similar bug ?

/cc @igor.drozdov @stanhu @robotmay_gitlab @plafoucriere

$ be rubocop --only Gitlab/PolicyRuleBoolean --parallel -- app/policies/ ee/app/policies/
Inspecting 124 files
.................................................................................................C..........................

Offenses:

ee/app/policies/ee/identity_provider_policy.rb:29:7: C: Gitlab/PolicyRuleBoolean: && is not allowed within a rule block. Did you mean to use &?
      rule { managed_group && last_group_saml_owner }.prevent(:unlink)
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

124 files inspected, 1 offense detected

Kept confidential for now, until we can talk more about #290710 (closed). Otherwise, this can be public as I don't think this is a security issue per se

Definition of done

• Remove usage of && in EE::IdentityProviderPolicy
• Backfill specs for the related rules
  • If it is determined that the usage of && is a security issue (gives users more access than they should have), open a security MR
  • If it is determined that the usage of && is NOT a security issue, mark this issue as non-confidential